Setting the right context in a python script?
As well as making the text object the context object you need to reselect it. (You did call deselect after all). An object can be context.active_object while not context.active_object.select  Some operators that work on all objects selected may only go thru the context.selected_objects list.

bpy.context.scene.objects.active = myobject
myobject.select = True
status = bpy.context.object.type
print(" bpy.context.object.type is: ", status)
status = bpy.ops.object.convert(target='MESH')          # fatal error

print("status after converting to a mesh is: ", status)